Computers consume electrical energy and reducing energy consumption reduces the costs of running computers. A company may run a very large number of computers. A small saving in energy consumption on each computer results in a large overall saving of energy and thus cost for the company.
It is known to provide control of the power state of a CPU of a computer. In one system, for example Intel's Speedstep, the CPU is designed to adopt, under the control of a power management program, any one of a plurality of power states P0 to Pn, where P0 is the highest power state and Pn is the lowest.
The value of n depends on the design of the CPU. If the computer is idle the operating system causes the computer to adopt the lowest power state Pn. If any activity is detected a higher power state P0 to P(n−1) is adopted according to the workload of the CPU. Normally the P0 state is adopted.